Help biasing P-Channel MOSFET

Discussion in 'The Projects Forum' started by JJM101, Jul 27, 2014.

  1. JJM101

    Thread Starter New Member

    Jul 27, 2014
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    Hi, I am trying to connect several batteries in series with P-Channel mosfets for a high power motor project I am working on (V = 48, I = up to 30A ). Basically, the idea is to switch the batteries into series with the MOSFETs when I want to run the motor, and if the MOSFETS are off, I can charge the cells individually.

    I have attached an image representing my current circuit. I pull the gate high with the source voltage and I ground the gate with another N channel mosfet.

    It works for the first few cells, but since I am going up to 48v, the specs for my P Channel (FQP47p06) have a Vgs max of +- 25V. And after the 7th 4.2V cell, I will exceed the Vgs max.

    So my question is, how can I properly bias the FETs after 25v without exceeding the max Vgs.
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Voltage divider so the gate doesn't pull all the way to ground.
     
  3. JJM101

    Thread Starter New Member

    Jul 27, 2014
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    Ronv, thanks for the reply. That was what I was thinking i could do, however, would the N-Channel I am using still function properly? Does the attached circuit diagram look like it would work? (disregarding the voltage divider values, i can calculate them later).
     
  4. ronv

    AAC Fanatic!

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    You can remove R11.
     
  5. JJM101

    Thread Starter New Member

    Jul 27, 2014
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    ronv, I removed R11 from the circuit, but that didn't work. But after looking at it I think i saw my mistake. You probably meant to say remove R10 because removing R10 worked! Attached is my updated circuit which halves the source voltage, hopefully it helps someone else in the future. Thanks for your help.
     
  6. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Sorry JJ. Like this:
     
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